The present invention relates to a polishing machine, more precisely relates to a polishing machine capable of polishing both sides (faces) of work pieces, e.g., silicon wafers, by an upper polishing plate and a lower polishing plate.
A conventional polishing machine for polishing both sides of work pieces, e.g., silicon wafers, is shown in FIG. 16. In FIG. 16, a lower polishing plate 200 and an upper polishing plate 202 are rotated in predetermined directions. Carriers 208, which are driven by an internal gear 204 and a sun gear 206, are provided between the polishing plates 200 and 202. Through-holes (not shown), in each of which a work piece to be polished is held, are bored in the carriers 208. Both sides (faces) of the work pieces held in the through-holes are simultaneously polished by the polishing plates 200 and 202.
The lower polishing plate 200 is mounted on a lower board 209 and rotated together with the lower board 209. The lower board 209 is rotatably mounted on a base 210 with a bearing 212. Torque of an electric motor 214, which rotates the lower board 209, is transmitted to the lower board 209 by transmission gears 216 and a cylindrical shaft 217.
The upper polishing plate 202 is rotated by torque of an electric motor 224, which is transmitted by transmission gears 218 and a shaft 219. The internal gear 204 is rotated by torque of an electric motor 226 by transmission gears 220 and a cylindrical shaft 221. Further, the sun gear 206 is rotated by torque of an electric motor 228 by transmission gears 222 and a shaft 223.
As shown in FIG. 17, a plurality of carriers 208 are mounted on the lower polishing plate 200, and a plurality of the through-holes 230, in which the work pieces will be accommodated and held, are bored in each carrier 208.
Gear teeth for engaging with the internal gear 204 and the sun gear 206 are formed on an outer edge of each carrier 208. By rotating the internal gear 204 and the sun gear 206, the carriers 208 are revolved and orbited around the sun gear 206 by difference of rotational speeds of the two gears 204 and 206.
The carriers 208, in each of which the work pieces are held in the through-holes 230, are sandwiched between the polishing plates 200 and 202, then the polishing plates 200 and 202, the internal gear 204 and the sun gear 206 are respectively rotated at predetermined rotational speeds. The work pieces are revolved and orbited around the sun gear 206 together with the carriers 208, so that the both sides of the work pieces can be polished simultaneously.
However, in the polishing machine shown in FIGS. 16 and 17, each of the carriers 208 is revolved on its own axis, so a peripheral speed of an inner part of the carrier 208 is different from that of an outer part. Further, the work piece held in the through-hole 230 of the carrier 208 is also revolved, so a peripheral speed of an inner part of the work piece is different from that of an outer part.
By the difference of the peripheral speeds of the carrier 208, the work pieces held in the inner part and the outer part of the carrier 208 cannot be polished uniformly, and abrasion spots are sometimes formed in the work pieces. Further, by the difference of the peripheral speeds of the work piece, the inner part and the outer part of each work piece cannot be polished uniformly, and abrasion spots are sometimes formed in the work piece.
Since the gear teeth of the carriers 208 are engaged with the internal gear 204 and the sun gear 206, abrasion dusts formed therebetween stick onto not only the carriers 208 but also polishing faces of the polishing plates 200 and 202.
To solve the above described disadvantages, an improved polishing machine, which is capable of polishing both sides of work pieces without revolving and orbiting carriers, was disclosed in U.S. Pat. No. 6,080,048. It is shown in FIG. 18.
In FIG. 18, an upper polishing plate 302 is rotated by a rotating unit 304 and vertically moved by a lifting unit 306. A lower polishing plate 310 is rotated by a rotating unit 308. One carrier 300 is sandwiched between the polishing plates 302 and 310. A plurality of through-holes 230, in each of which a work piece 100 is accommodated and held, are formed in the carrier 300.
The carrier 300 has a plurality of holes bored along an outer edge. By inserting pins 316, which are upwardly extended from a carrier holder 312, into the holes, the carrier 300 can be attached to the carrier holder 312.
The carrier holder 312 has a circular motion mechanism 320. The circular motion mechanism 320 includes: four bearing sections 318 outwardly extended from an outer circumferential face of the carrier holder 312; cranks respectively provided to the bearing sections 318; and a driving unit 340 capable of synchronously driving the cranks.
Each of the cranks includes: a rotatable eccentric arm 324 formed into a circular disk; and a shaft 322a arranged parallel to axial lines of the polishing plates 302 and 310 and having one end attached to the bearing section 318 and the other end eccentrically attached to the circular eccentric arm 324.
The driving unit 340 includes: shafts 322b, whose one ends are respectively attached to centers of the circular eccentric arms 324; sprockets 342 respectively attached to the other ends of the shafts 322b; a timing chain engaged with the sprockets 342; a gear 346 attached to one of the shafts 322b; a gear 350 engaged with the gear 346; and a motor 348 for rotating the gear 350.
In the polishing machine shown in FIG. 18, the polishing plates 302 and 310 are rotated in the predetermined directions by the motor 348 of the circular motion mechanism 320. Therefore, the carrier holder 312 sandwiched between the polishing plates 302 and 310 performs small circular motion, without revolving on its own axis, in a plane including the carrier 300. The peripheral speed differences of the carrier and the work pieces 100, which are caused by revolution of the carrier, can be solved.
Unlike the polishing machine shown in FIGS. 16 and 17, the carrier 300 has no gear teeth engaging with the internal gear and the sun gear. Therefore, no abrasion dusts are formed and stuck onto the carrier 300. Further, no abrasion dusts are stuck onto polishing faces of the polishing plates 302 and 310.
However, in the polishing machine shown in FIG. 18, the center of the carrier 300 is shifted a distance xe2x80x9cMxe2x80x9d from a coaxial line xe2x80x9cLxe2x80x9d of the polishing plates 302 and 310. The carrier 300 orbits around the line xe2x80x9cLxe2x80x9d without revolving its own axis. A radius of the circular orbit motion of the carrier 300 is equal to a distance between the shafts 322a and 322b (=xe2x80x9dMxe2x80x9d).
Since the carrier 300, whose center is shifted the distance xe2x80x9cMxe2x80x9d from the line xe2x80x9cLxe2x80x9d, performs the circular orbit motion without revolving, centers of gravity of the work pieces held in the through-holes 230 of the carrier 300 are located at different positions with respect to a center of gravity or a center of rotation of the upper polishing plate 302. Accordingly, uneven forces are applied to the work pieces 100 from the polishing plates 302 and 310, vibrations are generated while polishing, and polishing accuracy is lowered.
Since the carrier 300 must be broader than the polishing faces of the polishing plates. 302 and 310, the polishing machine must be large, and its manufacturing cost must be high. Namely, increasing efficiency by large-sized polishing machines is limited.
An object of the present invention is to provide a compact polishing machine capable of evenly applying a pressing force from an upper polishing plate to work pieces accommodated in through-holes of carriers.
To solve the problems of the conventional polishing machines, the inventors studied and found that polishing efficiency can be improved, without employing the large carrier, by sandwiching a plurality of small carriers, each of which has through-holes for accommodating work pieces, between an upper polishing plate and a lower polishing plate.
Further, they found that small circular motion of the carriers can be performed, without revolving, by independently driving the carriers between the upper polishing plate and the lower polishing plate. By performing the small circular motion, the pressing force can be evenly applied from the upper polishing plate to the work pieces.
To achieve the object, the polishing machine of the present invention has following structures.
Namely, the polishing machine comprises:
an upper polishing plate for polishing upper faces of work pieces;
a lower polishing plate for polishing lower faces of the work pieces;
means for rotating at least one of the polishing plates;
a plurality of carriers being provided around a center of gravity of the upper polishing plate and sandwiched between the polishing plates, each of the carriers having a through-hole, in which the work piece is accommodated;
means for independently performing circular motion or swing motion of the carriers without revolving on their own axes; and
means for controlling the performing means,
whereby centers of gravity of the work pieces, which are held by the carriers, are simultaneously moved close to a center of gravity of the upper polishing plate and simultaneously moved away therefrom, and moving distances of the centers of gravity of the work pieces are equal while the circular motion or the swing motion of the carriers.
The polishing machine may further comprise means for orbiting the carriers round a rotational axis of the lower polishing plate, and the rotating means may rotate the both of said polishing plates. With this structure, accuracy of polishing the work pieces can be improved, the work pieces can be fed and taken out at fixed place or places, and the work pieces can be automatically fed and taken out by a robot, etc.
Another polishing machine comprises:
a fixed upper polishing plate for polishing upper faces of work pieces;
a rotatable lower polishing plate for polishing lower faces of the work pieces;
means for rotating the lower polishing plate;
a plurality of carriers being provided around a center of gravity of the upper polishing plate and sandwiched between the polishing plates, each of the carriers having a through-hole, in which the work piece is accommodated;
means for independently performing circular motion or swing motion of the carriers without revolving on their own axes;
means for orbiting the carriers round a rotational axis of the lower polishing plate; and
means for controlling the performing means,
whereby centers of gravity of the work pieces, which are held by the carriers, are simultaneously moved close to a center of gravity of the upper polishing plate and simultaneously moved away therefrom, and moving distances of the centers of gravity of the work pieces are equal while the circular motion or the swing motion of the carriers.
In the polishing machine, the performing means may be located close to the lower polishing plate; and connecting sections, which are respectively formed in extended sections of the carriers projected from an outer edge of the lower polishing plate, may be respectively connected with connecting members of the performing means. With this structure, the circular motion or the swing motion of the carriers can be performed without revolving on their own axes.
In the polishing machine, the lower polishing plate may have a donut-shape with a center hole; a couple of the performing means may be respectively located close to an inner circumferential face of the center hole of the lower polishing plate and an outer circumferential face of the lower polishing plate; and connecting sections, which are formed in the carriers and located close to the inner circumferential face and the outer circumferential face of the lower polishing plate, may be respectively connected with connecting members of the performing means. With this structure, the circular motion or the swing motion of the carriers can be easily performed without revolving on their own axes.
In the polishing machine, the performing means may include eccentric arms, which are rotatable and in each of which a connecting pin connected with the carrier is eccentrically provided. With this structure, the circular motion or the swing motion of the carriers can be easily performed without revolving on their own axes.
In the polishing machine, the performing means may includes: eccentric arms, which are rotatable and in each of which a first connecting pin connected with the carrier is eccentrically provided; and swing arms, which are swingable and in each of which a second connecting pin is connected with the carrier at a position separated from the first connecting pin. With this structure, the swing motion of the carriers can be performed.
In the polishing machine, phases of the circular motion or the swing motion of the carriers provided to the lower polishing plate may be same, or an even number of the carriers may be provided to the lower polishing plate and the phases of the circular motion or the swing motion of the adjacent carriers may be shifted 180 degrees. With this structure, pressing force can be evenly applied from the upper polishing plate to the work pieces held or accommodated in the through-holes of the carriers.
In the polishing machine, each of the carriers may have a plurality of the through-holes. Further, each of the carriers may be formed into a diamond shape or a sector shape.
In the polishing machine of the present invention, a plurality of the carriers, which hold the work pieces, are sandwiched between the upper polishing plate and the lower polishing plate, so small-sized carriers may be employed. Therefore, a compact polishing machine, whose size is not limited by carriers, can be realized.
Further, the control means controls the performing means to simultaneously move the centers of gravity of the work pieces close to the center of gravity of the upper polishing plate and to simultaneously move the same away therefrom, and to make the moving distances of the centers of gravity of the work pieces equal while the circular motion or the swing motion of the carriers. With this control, a pressing force can be evenly applied from the upper polishing plate to the work pieces held or accommodated in the through-holes of the carriers. Therefore, accuracy of polishing the work pieces can be improved.
Especially, in the case of orbiting the carriers around a rotational axis of the lower polishing plate, the polishing accuracy can be further improved.